1. Technical Field
This invention relates to a refrigeration system and more particularly to an apparatus and method for improving refrigeration system efficiencies with improved subcooling control during varied ambient conditions.
2. Description of Prior Art
It has been known in the art of refrigeration systems that the net refrigerating effect in a refrigeration system can be improved by producing subcooling of the liquid refrigerant. Subcooling the refrigerant means that further energy is taken out of the liquid refrigerant and as a consequence it does not have to be removed by the expansion process in the cooling evaporator, thus improving the overall efficiency of the refrigeration system. As an example, it has been known that when a refrigerant leaving a condenser of a refrigeration system has been accumulated in a reservoir, it can then be circulated in the liquid form through another cooling section to produce subcooling of the refrigerant at a small additional operating cost. This method, however, requires an increased amount of refrigerant, which is undesirable.
In a refrigerator system, it is typical to equip a condenser with a flood control means which elevates the condensing pressure of a refrigeration system during low ambient temperatures by reducing the effective condenser surface that is available for condensing. This is accomplished by filling the condenser with liquid refrigerant when the pressure is not sufficient. These systems necessarily require increasing amounts of excess refrigerant to accomplish this flooding technique as the ambient temperature drops. This results in the use of additional refrigerant, which is undesirable because commonly used refrigerants, like Chloro-Fluoro-carbons ("CFCs"), are believed to increase the ozone depletion problem in the upper atmosphere. The additional refrigerant charge is generally lost when a leak occurs, which happens on the average several times over the life of a refrigeration system. This extra refrigerant usage may dramatically increase the amount of leakage of CFCs from refrigeration systems.
Refrigeration systems currently available also attempt to maximize the subcooling effect during the colder periods of the year, i.e., at lower ambient temperatures. These systems require increased amount of refrigerant to flood the condenser surfaces. One such system is described in U.S. Pat. No. 4,831,835, which performs subcooling during periods of low ambient temperature by utilizing a relatively complicated valve arrangement. This system ignores the subcooling at some ambient temperatures and instigates complicated measures to take advantage of subcooling in cold ambient temperatures. Subcooling of a refrigerant to a temperature that is closer to the ambient temperature of the systems will produce better efficiencies at all times of the year. Thus, subcooling within the condenser itself at all times, i.e., at all ambient temperatures, is a very desirable feature to have in a refrigeration system, which has gone unrecognized in the art.
U.S. Pat. No. 4,621,505 also describes an arrangement to improve the subcooling effects during low ambient conditions. With respect to subcooling at higher ambients, this patent suggested that in summer operations when the ambient is above 85 to 90 degrees F., the condensation temperature and head pressures will be higher and little or no economic benefit can be expected. The need to benefit from subcooling has been known for some time in the refrigeration industry; however, to date, no method for achieving subcooling in a condenser at all ambients (high or low) has succeeded in the market place.
Another type of a subcooling system is disclosed in U.S. Pat. No. 4,136,528. It describes a system which provides subcooling to a degree that is sufficient to insure that the expansion valves operate properly in colder ambient conditions. This system fails to recognize that the subcooling in the summer time can provide further energy savings. This is another example where the need to subcool has been recognized for colder ambients but the value of subcooling in higher ambients has been ignored.
The attempts of the past to build-in subcooling into a condenser have failed to recognize the necessity of holding the refrigerant in the liquid state for some time before allowing it to leave the condenser. In order to make thermal expansion valves function, hold-back valves have been used in the condensate line leaving the condenser to elevate the condensing pressure during low ambient conditions. This method produces liquid subcooling when the condenser is flooded with liquid. Once the industry recognized the benefits of subcooling, various methods have been utilized to subcool the refrigerant in colder ambient conditions. The hold-back valves used for this purpose have throttling ranges from fully open to fully closed of 20 to 60 psi have been used, which meant that an additional inefficiency of higher condensing pressures during higher ambient and higher flow conditions were introduced.
The present invention provides a refrigeration system and method for increasing the subcooling effect of the condenser while utilizing minimal amounts of refrigerant. This system provides subcooling of the condenser during all ambient temperatures.